Field of the Invention
The present invention relates to an active matrix organic light emitting display, and more particularly, to a method for repairing a defective pixel of an organic light emitting display.
Discussion of the Related Art
An active matrix organic light emitting display includes organic light emitting diodes (hereinafter, abbreviated to “OLEDs”) capable of emitting light by itself and has advantages of a fast response time, a high light emitting efficiency, a high luminance, a wide viewing angle, and the like.
The OLED serving as a self-emitting element includes an anode electrode, a cathode electrode, and an organic compound layer formed between the anode electrode and the cathode electrode. The organic compound layer includes a hole injection layer HIL, a hole transport layer HTL, a light emitting layer EML, an electron transport layer ETL, and an electron injection layer EIL. When a driving voltage is applied to the anode electrode and the cathode electrode, holes passing through the hole transport layer HTL and electrons passing through the electron transport layer ETL move to the light emitting layer EML and form excitons. As a result, the light emitting layer EML generates visible light.
The organic light emitting display arranges subpixels each including the OLED in a matrix form and adjusts an amount of light emitted by each OLED depending on a gray scale of video data. Each subpixel includes a circuit unit for driving a light emitting unit, i.e., the OLED. The circuit unit includes a driving thin film transistor (TFT) controlling a driving current flowing in the OLED and a plurality of switching TFTs for programming a gate-source voltage of the driving TFT in conformity with a desired gray level.
The number of TFTs and signal lines formed on a display panel of the organic light emitting display is more than other display devices, and the organic light emitting display has more complex configuration than the other display devices. Therefore, a defect is frequently generated in the circuit unit of the organic light emitting display. In the organic light emitting display, the subpixel including the defective circuit unit does not normally emit light and is recognized as a dark spot. However, because a subpixel of a specific color having a relatively high transmittance has the higher visibility of the dark spot than the subpixels of other colors, a countermeasure is required. Hence, a dummy pixel structure shown in FIG. 1 was proposed.
In FIG. 1, “A” demotes a dummy pixel, and “B” demotes a normal pixel. The normal pixel B is formed in a display area, in which an image is implemented, and the dummy pixel A is formed in a non-display area outside the display area. The dummy pixel A is a pixel, which is additionally formed so as to perform a repair process. In the related art dummy pixel structure, when a defect is generated in a circuit unit of the normal pixel B, the repair process is performed to connect a light emitting unit of the normal pixel B to a circuit unit of the dummy pixel A, thereby causing the normal pixel B to emit light. Hence, the problem of the dark spot is removed.
The related art dummy pixel structure requires the separate dummy pixel A on the display panel of the organic light emitting display, so as to remove the defect. However, when the dummy pixel A is formed on the display panel, an occupation ratio (i.e., an aperture ratio) of the display area of the image displayed on the display panel is reduced by a formation area of the dummy pixel A.